In light-emitting devices, a P-N junction diode having a characteristic of converting electrical energy into light energy may be manufactured by combining periodic table Group 3-5 elements or 2-6 elements, and various colors are realized by adjusting a combination ratio of compound semiconductors.
For example, nitride semiconductors are attracting much attention in the development field of light devices and high output electronic devices due to high thermal stability and energy having a wide bandgap. Particularly, blue light-emitting devices, green light-emitting devices, ultraviolet (UV) light-emitting devices, and red light-emitting devices using the nitride semiconductors have been commercialized and are being widely used.
Such light-emitting devices may realize various colors such as red, green, blue, and UV and may realize white light having good efficiency by using fluorescent materials or combining various lights emitted. Therefore, the light-emitting devices have low power consumption, a semi-permanent lifetime, a fast response time, safety, and environmental affinity in comparison with fluorescent lamps and incandescent lamps.
Examples of a method of realizing white light include a method using a single chip and a method using a multichip. For example, in a case where white light is realized by using the single chip, a method of obtaining white light by exciting at least one phosphor with light emitted from a blue light-emitting diode (LED) or an UV LED is being used. Alternatively, in the multichip, for example, there is a method of manufacturing a multichip by combining three kinds red (R), green (G), and blue (B) chips.
A retina of a human body includes a B cone cell, a G cone cell, and an R cone cell. A level of each of electrical signals varies based on a degree to which the three cone cells are excited by external light, and brains combine the electrical signals to determine a color.
The related art uses a blue LED having a center wavelength of 440 nm to 450 nm, for increasing an energy efficiency of a light source.
For example, FIG. 1A is an exemplary diagram showing a wavelength spectrum C1 of a first related art light-emitting device package with respect to an emission wavelength S of sunlight. Referring to FIG. 1A, an energy ratio HC of a first wavelength range H of about 415 nm to 455 nm occupies an area which is larger than an energy ratio BC of a second wavelength range B of about 465 nm to 495 nm.
For example, in the related art, with respect to sunlight, the energy ratio HC of the first wavelength range (415 nm to 455 nm) area is about 98%, and the energy ratio BC of the second wavelength range (465 nm to 495 nm) area is merely about 54%.
Moreover, FIG. 1B shows the wavelength spectrum C1 of the first related art light-emitting device package, a wavelength spectrum of a green phosphor G1 applied thereto, and a wavelength spectrum of a red phosphor R1 applied thereto.
According to recent research, in a case where a visual cell of a human body is exposed to light having the first wavelength range H of about 415 nm to 455 nm, an eye-hazardous effect is applied to eyes and is accumulated during one's lifetime. It is checked that the eye-hazardous effect causes age-related macular degeneration and damages a vision of persons. The age-related macular degeneration is a main cause of vision loss of old age, but occurs in young age recently. It has been known that if visual impairment starts due to the disease, it is unable to recover previous vision.
In order to decrease hazardousness within the first wavelength range H of about 415 nm to 455 nm, some researches have attempted to use a filter in front of an LED or wear glasses with a filter equipped therein. In the attempt, a wavelength range harmful to eyes of the first wavelength range H of about 415 nm to 455 nm, and in addition, another problem where a blue range necessary for manufacturing a white light source and the second wavelength range B of about 465 nm to 495 nm beneficial to control the one-week rhythm of a human body are removed occurs.
FIG. 2 shows special CRI data of the first related art light-emitting device package. According to FIG. 2, a value of R9 (pure red) which is one of indicators indicating the quality of a light source is −11.9, and due to this, there is a problem where reflected light similar to sunlight is generated.
FIG. 3 shows a wavelength spectrum C2 of a second related art light-emitting device package, a wavelength spectrum of a green phosphor G2 applied thereto, a wavelength spectrum of a second red phosphor R2 applied thereto, and a wavelength spectrum of a third red phosphor R3 applied thereto. Generally, a phosphor where a photoluminescence (PL) wavelength is a long wavelength has light efficiency which is lower than that of a phosphor having a short wavelength, and thus, is reduced in luminous flux.
The second related art cannot satisfy requirement “R9>0” of business community by using only the second red phosphor R2 (a peak wavelength of 610 nm) having a short wavelength. Therefore, by using the third red phosphor R3 (a peak wavelength of 625 nm) having a long wavelength and low energy efficiency together, it has been attempted to improve an R9 indicator despite the luminous flux being lost.
Therefore, the related art has a technical limitation which cannot satisfy both a technical characteristic for enhancing the luminous flux and a technical characteristic for improving (for example, R9>0) a special CRI index.